WINNIPEG, Manitoba/OTTAWA, March 20 (Reuters) - Nearly half of Canadians want to deport people who are illegally crossing into Canada from the United States, and a similar number disapprove of how Prime Minister Justin Trudeau is handling the influx, according to a Reuters/Ipsos opinion poll released on Monday.

A significant minority, four out of 10 respondents, said the border crossers could make Canada "less safe," underlining the potential political risk for Trudeau's Liberal government.

The increasing flow of hundreds of asylum-seekers of African and Middle Eastern origin from the United States in recent months is becoming a contentious issue in Canada.

Although there has been broad bipartisan support for high levels of legal immigration for decades in Canada, Trudeau is under pressure over the flow of the illegal migrants.

He is questioned about it almost every time he appears in parliament, from opponents on the left, who want more asylum-seekers to be allowed in, and critics on the right, who say the migrants pose a potential security risk.

Canadian opposition parties seized on the poll results, with both those on the left and the right saying they underscored their positions.

Canadians appeared to be just as concerned about illegal immigration as American, according to the poll, which was conducted between March 8-9. Some 48 percent supported "increasing the deportation of people living in Canada illegally." (For graphics on asylum process, immigration poll see http://tmsnrt.rs/2nyY8CJ)

When asked specifically about the recent border crossings, the same number - 48 percent - said Canada should "send these migrants back to the U.S." Another 36 percent said Canada should "accept these migrants".

In the United States, where President Donald Trump was elected partly on his promise to boost deportations, 50 percent of adults supported "increasing the deportation of illegal immigrants," according to a Reuters/Ipsos poll conducted in the same week.

Illegal migrants interviewed by Reuters in Canada said they had been living legally in the United States and had applied for asylum there. But they fled for fear of being enmeshed in Trump's immigration crackdown.

Kevin O'Leary and Kellie Leitch, top contenders to be leader of the official opposition right-leaning Conservative Party, both said the poll showed they were right to demand Ottawa deter border crossers.

Like Trump, O'Leary is a brash businessman and television personality with little experience of politics.

The left-leaning opposition New Democrats said given the poll showed Canadians wanted asylum seekers to cross the border legally, Ottawa should suspend an agreement with the United States whereby Canada turns back refugees from the United States if they try to make claims at border crossings.

WARMING WEATHER POSES RISK

Support for deportations was strongest among men, adults lacking a college degree, people who are older and those with higher levels of income.

"There are so many people in the world who want to come in and go through the right channels," said Greg Janzen, elected leader of a Manitoba border municipality that has seen many crossers. "That's what's pissing most people off. These guys are jumping the border," he said.

Forty-six percent feel the influx would have no effect on safety, while 41 percent said it would make Canada less safe, according to the poll.

"Refugees are much more welcomed when we have gone and selected them ourselves as a country, as opposed to refugees who have chosen us," said Janet Dench, executive director of Canadian Council for Refugees.

Of those polled, 46 percent disagreed with how Trudeau was handling the situation, 37 percent agreed, while 17 percent did not know. In January, a separate Ipsos poll found 59 percent of Canadians approved of Trudeau, while 41 percent disapproved.

Trudeau faces no immediate threat, since the next elections are not until 2019. His office declined to comment on the poll.

Brian Lee Crowley, head of the Macdonald-Laurier Institute public policy think-tank, said the number of illegal migrants could spike as the weather warms, and "if people become convinced there's a large uncontrolled flow of illegal immigrants, I think that will be a very serious political issue for the government."

Authorities dismiss the idea they are being lax.

Dan Brien, spokesman for Public Safety Minister Ralph Goodale, said trying to slip across the border "is not a 'free' ticket to Canada," and noted all the asylum-seekers are immediately arrested.

"If they are found to be inadmissible without a valid claim, deportation procedures are begun," he said when pressed on the poll. Those who cannot be identified, are a flight risk or pose a public danger can be detained, he added.

According to a separate Ipsos poll, 23 percent of Canadians listed immigration control as among the top national issues in March, up from 17 percent in December. It ranks behind healthcare, taxes, unemployment and poverty as top concerns.

Ottawa set an immigration target of 300,000 for 2017, or just under 1 percent of the population, the same level as 2016. It reduced the 2017 target for resettled refugees to 25,000 from 44,800 in 2016, when it welcomed 25,000 Syrian refugees.

The Reuters/Ipsos poll was conducted online in English and French throughout Canada. It included responses from 1,001 people 18 years or older. Individual responses were weighted according to the latest population estimates, so that the results reflect the entire population.

The poll has a credibility interval, a measure of accuracy, of 4 percentage points.